Manufacture of semiconductor devices requires various heat treatment steps under controlled environments. Typically, a large number of semiconductor wafers carried by a wafer boat made of heat resistant material such as quartz glass is received in a processing chamber (such as a diffusion chamber and a reaction chamber) defined inside a pressure vessel typically made of heat resistant material such as quartz glass, and process gases are introduced into the processing chamber. A heating arrangement is placed around the processing chamber, and a desired process is conducted in the processing chamber with the semiconductor wafers heated to a desired temperature.
The heating arrangement for such a heat treatment system typically uses a coil-shaped electroresistive heater element, and the heater element is supported by spacers made of alumina or other refractory material. Additionally, insulating material typically consisting of ceramic fibers is filled in the gap defined between the exterior of the heating arrangement and the outer casing surrounding the processing chamber.
However, such a conventional heat treatment system using a electroresistive heater element has a relatively large heat capacity, and it is not possible to rapidly heat or cool the processing chamber. In other words, because of the time lag in heating or cooling the processing chamber, it is difficult to achieve an accurate and responsive temperature control. In particular, because the insulating material prevents rapid cooling, it is not possible to lower the temperature of the processing chamber as rapidly as desired. This is detrimental in reducing the turnaround time of the heat treatment system, and achieving a high quality heat treatment.
Also, according to a conventional heat treatment system using an electroresistive heater element, it is difficult to achieve an even temperature distribution in the processing chamber. This is particularly significant in view of the increasing demand for semiconductor wafers having large diameters. Handing such large semiconductor wafers requires a correspondingly large processing chamber, and an electroresistive heater element is often unable to heat the central part of the processing chamber as much as the peripheral part of the processing chamber.
Furthermore, an electroresistive heater element tends to produce particles during use, and this may seriously contaminate the clean room environment which is required for semiconductor manufacturing processes.